A hybrid electric vehicle (HEV) is a vehicle that can be propelled by an engine and a traction battery. A plug-in hybrid electric vehicle (PHEV) is a HEV in which the traction battery can be charged by being plugged in to an external power source. A battery electric vehicle (BEV) is a vehicle that does not include an engine and is propelled only by a traction battery. HEV's, PHEV's and BEV's are three examples of vehicles that are at least partially propelled by a traction battery. In such applications, the vehicles typically include a ventilation system to expel heat, air and gas away from the traction battery to maximize efficient operability of the battery.